1. Field of the Invention
The present invention relates to a monitoring system for monitoring a serial transmission line by receiving data flowing through the serial transmission line and by analyzing the received data in accordance with a predetermined protocol or data format for serial transmission.
Before discussing the present invention, we shall indicate the meaning of the following codes to be used throughout this specification.
ASCII : American Standard Code for Information Interchange PA0 EBCDIC: Extended Binary Code Decimal Interchange Code PA0 EBCDIK: A code created by Hitachi Co., Ltd. based on PA0 HEX : Hexadecimal Notation Code PA0 JIS7: Japanese Industrial Standard 7 Bit Code PA0 JIS8: Japanese Industrial Standard 8 Bit Code PA0 (1) Conventional monitoring systems are unable to convert the display data into other codes (for example, HEX) for monitoring. PA0 (2) In the same manner as described above, it is not possible to convert data into other codes temporarily for monitoring. PA0 (3) It is not possible to convert a predetermined range of the data, not the whole of the data, into another code for monitoring.
EBCDIC.
2. Description of the Prior Art
Known as a monitoring system for a serial transmission line are an on-line monitor and an on-line scope. Generally in these types of monitoring system, transmission data are stored in a memory, then read successively from that memory and converted into display data in accordance with a preset protocol or format and then the thus converted data is displayed.
As long as this type of simple conversion method is used, however, an erroneous display output may occur typically in JIS7 and EBCDIK coding in which the same transmission data has different meanings depending on whether a shift-in mode is employed or shift-out mode. For example, when the JIS 7 code 41.sub.H is inputted as transmission data, the alphabetic character "A"is displayed in the shift-in mode, but the katakana character " " is displayed in the shift-out mode. When the system is set so that the display output is always in the shift-in mode at the start of monitoring, and a shift-out code (SO) flows through the serial transmission line prior to the start of the monitoring, the monitoring system will display the input data in the shift-in mode (alphabet mode), making an erroneous display. This is because, even though the input data should all be outputted on the shift-out side (katakana mode), the monitoring starts after the shift-out code (SO) has flowed.
Furthermore, among the transmission data, even non-transmission type data, for example, error-checking BCC (Block Check Character) data, is transmitted as transmission type data (when the raw data has been converted into a code such as JIS8 or ASCII). In such cases, when the received data are all displayed by a predetermined code conversion, there is a defect in that it is difficult to determine the transmission type data. For example, when the received,, data is all converted into JIS8 code and displayed, if the JIS8 code is specified, the data 43.sub.H received as BCC data would be converted into the character "B" and displayed, since the JIS8 code is specified. That is, when the user checks BCC, he normally checks BCC in the form of raw data (HEX), so that there is a disadvantage that the user must convert the character "B" again into HEX before checking.
Conventional monitoring systems also have the following disadvantages.
Furthermore, in the usual monitoring systems, all the received data stored in a memory are hardy required later, and in many cases the memory contains unnecessary received data. In particular, when analyzing trouble on the serial transmission line, in many cases only a limited portion of the data is really necessary.
However, conventional monitoring systems for a serial transmission line do not have a function for selecting data stored in a memory, so that in order to store a desired portion of the data, all the collected data must be stored. This causes the following disadvantages.
(1) Since unnecessary data is stored, the storage capacity which can be used in monitoring the transmission line is insufficient. Furthermore, an increase in the memory capacity to make up for this shortage leads to an increase in cost, and the use of an external storage unit such as a cassette magnetic tape recorder is inconvenient from the point of view of operation and portability.
(2) Retrieval of necessary data from data including unnecessary data leads to an increase in processing time.
(3) Storage of data in an external storage unit causes shortages of storage medium or cost increases due to increased storage capacity.
(4) When data is stored in an external storage unit, a large amount of time is needed for recording and/or reproduction processing.
In a conventional monitoring system of this type for a serial transmission line, methods such as the following have been adopted to display the condition of control line data.
(1) With respect to writing to memory: The control line data is sampled periodically while the serial data is being received and all the results of this sampling are stored in the control line data memory in the same manner as the serial data. Then, the stored control line data is read out from the memory and is reproduced on the display screen while maintaining a time relationship of the control line data with the serial data read out from the data memory.
However, this type of monitoring system is arranged so that all the sampled control line data are stored in the control line data memory. As a consequence, there is a disadvantage in that a control line data memory having a memory capacity as large as the serial data memory is necessary.
(2) With respect to the display format: When the control line data is being displayed, a display format like those shown in FIG. 1 or FIG. 2, for instance, is adopted.
The display format shown in FIG. 1 indicates the conditions of the respective control lines DTR, RTS, DSR and CTS with wave forms corresponding to the serial data series SD and RD shown by the O mark.
In the display formats shown in FIG. 1 and FIG. 2, SD denotes Send Data, RD Received Data, DSR Data Set Ready, CTS Clear to Send, DTR Data Terminal Ready and RTS Request to Send. On this display format, however, the majority of the area of the display screen is occupied by the control line data display, so that there is a disadvantage that the volume of serial data which can be displayed within the display screen is greatly reduced.
The display format shown in FIG. 2 indicates a change in the condition of the control line data by the display mode, i.e., whether the serial data is displayed in a normal dislay mode or in a reverse display mode. This display format, however, has a disadvantage in that the conditions of a plurality of control line data cannot be displayed.
Moreover, particularly when displaying received data, the above described conventional systems sometimes display the data in real time. In this case, the received data is displayed immediately.
With this type of display system, however, when the transmission speed on the serial transmission line is slow (for example, 1,200 bps (bits per second)), the user is able to confirm visually the display data even when the received data is displayed immediately. However, on the other hand, when the transmission speed is fast (for example, 19,200 bps), the user is unable to keep up with the display data when it is displayed in real time. This causes a disadvantage in that it is extremely difficult to determine the type of data which has been transmitted.
In order to avoid the above-mentioned disadvantages, a method may be considered in which the displayed data is temporarily fixed or frozen, so that the data can be measured. In this case, however, there is a disadvantage that the data display becomes intermittent and therefore it is possible to understand the mutual relationship only between data displayed on the same screen, and accordingly it is not possible to determine the relationship between data on one displayed image screen and the data on the other picture.